(a) Field of the Invention
The present invention relates to a hydraulic pressure control system of an automatic transmission capable of adjusting line pressure of the hydraulic system.
(b) Description of the Related Art
Generally, a conventional automatic transmission for a vehicle includes a multi-stage gear shift mechanism connected to a torque converter, and a plurality of friction elements actuated by hydraulic pressure for selecting a gear stage of the gear shift mechanism.
In such hydraulic control systems, hydraulic pressure generated by a hydraulic pump is selectively supplied to each friction element by a plurality of control valves such that automatic shifting is realized in accordance with a driving state of the vehicle and engine throttle opening.
The above hydraulic control system generally comprises a pressure regulating controller for controlling hydraulic pressure generated by the hydraulic pump, manual and automatic shift controllers for selecting a shift mode, a hydraulic pressure controller for controlling shift response and shift quality, a damper clutch controller for actuating a damper clutch of the torque converter, and a hydraulic pressure distributor for supplying an appropriate amount of hydraulic pressure to each of the friction elements.
The hydraulic pressure distributor distributes a variable amount of pressure in accordance with an ON/OFF or duty operation of solenoid valves by a transmission control unit such that shift control is realized.
FIG. 4 shows a conventional line pressure control system in such a hydraulic system.
As shown in FIG. 4, the hydraulic pressure generated by the hydraulic pump 200 is adjusted so as to have a predetermined level of line pressure, by a regulator valve 202. Partially, the regulated line pressure is adjusted by a torque converter control valve 204 and then supplied to a damper clutch valve 206 under control of the damper clutch solenoid valve S1, and partially the pressure level of the line pressure is reduced so to be supplied to the damper clutch control valve 206 or to friction elements via hydraulic pressure control means and hydraulic pressure distribution means by driver""s manipulation of a manual valve 210, that converts ports so as to direct the pressure to appropriate lines.
The regulator valve 202 is controlled by pressure from the manual valve 210 via a forward pressure line 212 in ranges of N, D, 2, and L; by pressure via a pressure line 214 which is connected to the friction elements that operate in third and fourth speed of D range; and by reverse pressure via a reverse pressure line 216 connected to the main valve 210 in range R.
In this conventional line pressure control system, however, since the pressure control is performed by pressure from the lines 212, 214, and 216 biasing the valve spool of the manual valve, and an elastic force of a spring 218, it is difficult to electrically and actively control the line pressure, resulting in mileage reduction of the vehicle.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a line pressure control system of an automatic transmission capable of maintaining optimal line pressure in a present running condition so as to improve gasoline mileage, and making a line pressure control range broader using a full line pressure control mechanism by adapting a line pressure control solenoid valve.
To achieve the above object, the line pressure control system of an automatic transmission of the present invention comprises a hydraulic pump for generating hydraulic pressure, a regulator valve for adjusting the pressure from the hydraulic pump to a predetermined level, a torque converter control valve for adjusting a partial pressure from the regulator valve, a damper clutch valve receiving the adjusted pressure from the torque converter control valve for feeding the pressure to a damper clutch, a damper clutch solenoid valve for controlling the damper clutch valve, a reducing valve for reducing a partial pressure from the regulator valve and then supplying the reduced pressure to the damper clutch control valve, wherein the regulator valve comprises a valve body, a first and a second valve spool coaxially inserted into the valve body, a sleeve encapsulating the second valve spool, and a coil spring interposed between the first and the second valve spools.